How many useless PCs do you have sitting around? Whether they're too old and slow or simply stopped working one day, cast-off tower and minitower machines are a plague on the land. So I decided to repurpose one by stripping it to its essential form?an empty box?and rebuilding it as a self-powered subwoofer. This is an inherently bad idea. Metal clangs and vibrates; speaker cabinets should be nonresonant. PC cases have more holes in them than the Godfather's enemies; speaker cases need to be airtight. Metal is inconvenient to work with; wood cuts easily. None of those practical considerations matter once you get the burning desire to mod a PC case in a totally unusual way. If you're like me and, for whatever reason, can't resist the temptation, here's how it's done. I had a number of dead PCs in the basement, including a tall, thin tower and a couple of short, squat Hewlett-Packard machines. I chose an HP for its case's wider front panel, because I wanted a front-firing speaker. ExtremeTech